Special Circumstances (WK 4)

Question 1

Which structure does the coronary venous blood use, and to drain into where?

Answer 1

Uses the coronary sinus to drain into the right atrium.

Question 2

What happens in coronary heart disease?

Answer 2

Area of cardiac muscle deprived of blood due to a blockage in a coronary artery.

Question 3

What are some common areas of blockage in CHD?

Answer 3

• Left coronary artery

- left anterior descending artery.

Question 4

What are the special adaptations of coronary circulation?

Answer 4

• High capillary density
• High basal blood flow
• High O2 extraction rate

Because of this, the only way to supply extra O2 to the myocardium is by increasing the blood flow and thus o2 content to it.

Question 5

What intrinsic mechanisms control coronary blood flow?

Answer 5

1. Reduced P02= vasodilation of c arteries.
2. Metabolic hyperaemia- matches flow to demand
3. Adenosine- vasodilator.

Question 6

What extrinsic mechanisms control coronary blood flow?

Answer 6

Sympathetic vasoconstrictor tone Overidden by metabolic hyperaemic drive.
So sympathetic stimulation causes- coronary Vasodilation

Adrenaline- B2 adrenoceptors that can cause vasodilation

Question 7

When does peak coronary artery blood flow occur?

Answer 7

in Diastole. A very fast HR (arrhythmia) means reduced coronary blood flow.

Question 8

Which type of arteries is the brain supplied by?

Answer 8

• internal Carotid arteries

- Vertebral arteries

Question 9

What is the circle of Willis?

Answer 9

Basal arteries (formed from vertebral arteties) and carotid arteries anastomose to form the circle of willis.
Major coronary arteries emerge from the circle.

Question 10

What are the two types of stroke? Explain each type.

Answer 10

Hemorrhagic- blood leaks out of damaged artery wall.

Ischaemic- Blood clot forms an atheroma on vessel wall. could also be an emboli stuck in the cerebral arteries.

Question 11

What happens in auto-regulation of cerebral blood flow in response to MAP?

Answer 11

MAP too high- Vasoconstriction
MAP too low- Vasodilation

Autoregulation maintains cerebral flow in any MABP changes between 60 and 160mmHg.

Question 12

What happens in the brain if MAPBP is below 50mmHg?

Answer 12

Confusion, fainting.

Brain damage if not quickly sorted

Question 13

What other factors regulate cerebral blood flow?

Answer 13

Higher PCo2–> Causes cerebral vasodilation

Question 14

What is regional hyperaemia?

Answer 14

Blood flow increases to areas of the brain that are more active.

Question 15

What is the effect of intracranial pressure on cerebral blood flow?

Answer 15

Decreases cerebral blood flow.

Question 16

What are some features of the blood brain barrier that helps it to maintain brain functionality?

Answer 16

V permeable to 02 and CO2
Impermeable to ions, proteins etc (protects brain from fluctuating ion levels in blood)
Glucose crosses barrier via diffusion through carrier molecules.

Question 17

What systemic adaptations protects the lungs from pulmonary oedema?

Answer 17

Systemic absorption exceeds filtration rate.

Question 18

What is the effect of hypoxia on pulmonary arterioles?

Answer 18

Vasoconstriction. Diverts blood away from poorly ventilated areas of the lung.

Question 19

What happens to skeletal muscle blood flow in exercise?

Answer 19

• Metabolic hyperaemia overides vasoconstrictor tone- Vasodilation.
• Circulating Adrenaline stimulates B2 adrenoceptors- vasodilation
• Increased cardiac flow= increased blood flow to skeletal muscle.

Overall effect- increased blood flow to skeletal muscle.

Question 20

What does the skeletal muscle pump do?

Answer 20

Contraction of large limb muscles increases Venous Return to the heart.
Helps in: Postural hypotension. fainting.

Question 21

What are varicose veins?

Answer 21

Pooling of blood in lower limbs if valves become incompetent.
Doesn’t usually lead to lower CO–> Cos of compensatory increase in blood volume